Need some engine advice....

[Ski 61701]

Go to UEMpistons.com and look for static compression chart. It's simple to use, takes a lot of the guessing of things and save you time n $$$ long term here.
even though it shows 9.9.1 comp, the cranking pressure could be through the roof giving you the current problems

 

[Ski 61701]

I'll have to check out that website to see if I can learn anything. Was hoping someone on here had a magic wand to tell me if what he wrote down was close.
No doubt if I continued running a mix of 110 I could get this thing really screaming. Advance the timing to 35, put in some lighter springs, play with the accelerator cams and squirters.
The power feels awesome now just not having the detonation and not losing power because of that.

You'll get it figured out once we know what you actually have.. it removes a lot of flipping stuff on the wall seeing what sticks kinda repair

 

[451Mopar]

Well, I'm at a loss? I don't see cylinder pressures that high hear in Denver because of the altitude.

Looking at some of the numbers, to get 9.9:1 compression the pistons would need to have a 22 to 23cc dish?
And estimated cranking pressures around 156 psi if the intake closes at 72.5 degrees ABDC? Based off the 285 @ 0.006" timing, 112 LSA installed at 110.

I can see where the pistons may be custom because they are only 0.010" oversize, and should be dished to lower compression, but if they are flat top pistons, the compression ratio would be closer to 11.4:1 compression, and that would make the cranking pressures higher?
If the can was installed with the timing as indicated on the Comp cam card, the cam would be advanced about 4-degrees?,

I think to get the 180 psi cranking pressures, either the lifters are bleeding down at the low cranking speed, or you compression is closer to 11:1?

 

[PRHeads]

I’m not understanding the logic of the 3 pumps and done on the compression test.
I’ve never seen one max out in 3 pumps.

Why guess?
Just crank it until the needle stops gaining. In my experience, it usually takes 7-8 pumps.

 

[PRHeads]

I think to get the 180 psi cranking pressures, either the lifters are bleeding down at the low cranking speed

A very strong possibility....... and it could even be happening a bit while it’s running.

The bottom line is........ it currently pings on the gas you have there.
The tune up parameters seem very normal.

So the answer is, yes....... that basic combo of parts, in your car, with the gas you can find locally........ has too much running compression to not ping.

Detuning the motor to the point where it doesn’t ping is a much worse evil(from a drivability standpoint) than if it had just been built with a lower CR that would run happily on the available gas, without the motor being detuned.

 

[hunt2elk]

Its doesn't make sense to me to try a hotter plug if you have detonation.. When you are dealing with detonation your best results will be running the coldest plug you can get run. Putting a hotter plug may have made the issue worse if you did it at the same time as your dist recurve, they may have canceled each other out.

The motor had NGK6's in it when it came back to me. Brian had me go one step colder to NGK7's.

 

[Curiousyellow71]

The motor had NGK6's in it when it came back to me. Brian had me go one step colder to NGK7's.

That was the right thing to try...I had forgotten NGK goes colder w bigger number....
We crank them 2 till we get a max compression on the gauge. Counting never made sense to me, should only matter that it gets cranked enough to simulate running. You can go to wallace racing and if you put your barometric pressure in during the test, it will give you a estimate in psi based on your intake valve closing and static compression.
http://www.wallaceracing.com/calc-crank-press.php

 

[beanhead]

I’m not understanding the logic of the 3 pumps and done on the compression test.
I’ve never seen one max out in 3 pumps.

Why guess?
Just crank it until the needle stops gaining. In my experience, it usually takes 7-8 pumps.

That was the right thing to try...I had forgotten NGK goes colder w bigger number....
We crank them 2 till we get a max compression on the gauge. Counting never made sense to me, should only matter that it gets cranked enough to simulate running. You can go to wallace racing and if you put your barometric pressure in during the test, it will give you a estimate in psi based on your intake valve closing and static compression.
http://www.wallaceracing.com/calc-crank-press.php

Holy guacamole you mean I've been doing something right all this time?!

 

[Kern Dog]

I’ve never seen one max out in 3 pumps.

Ask my Wife.

 

[PRHeads]

Ask my Wife.

I though that was “one and done”

 

[Kern Dog]

 

[andyf]

A very strong possibility....... and it could even be happening a bit while it’s running.

The bottom line is........ it currently pings on the gas you have there.
The tune up parameters seem very normal.

So the answer is, yes....... that basic combo of parts, in your car, with the gas you can find locally........ has too much running compression to not ping.

Detuning the motor to the point where it doesn’t ping is a much worse evil(from a drivability standpoint) than if it had just been built with a lower CR that would run happily on the available gas, without the motor being detuned.

Yeah I agree. If the engine pings then it pings and you'll just have to deal with it regardless of what your cranking compression is. If you can buy AV gas in your local area then that might be a solution. Just mix it 50/50 with pump gas premium and see if that works. It is a hassle to always buy AV gas but not as big of a hassle as rebuilding the engine.
You can also try various timing curves and make sure that your air fuel ratio is correct and all those sorts of things.

 

[hunt2elk]

A very strong possibility....... and it could even be happening a bit while it’s running.

The bottom line is........ it currently pings on the gas you have there.
The tune up parameters seem very normal.

So the answer is, yes....... that basic combo of parts, in your car, with the gas you can find locally........ has too much running compression to not ping.

Detuning the motor to the point where it doesn’t ping is a much worse evil(from a drivability standpoint) than if it had just been built with a lower CR that would run happily on the available gas, without the motor being detuned.

A very strong possibility....... and it could even be happening a bit while it’s running.

The bottom line is........ it currently pings on the gas you have there.
The tune up parameters seem very normal.

So the answer is, yes....... that basic combo of parts, in your car, with the gas you can find locally........ has too much running compression to not ping.

Detuning the motor to the point where it doesn’t ping is a much worse evil(from a drivability standpoint) than if it had just been built with a lower CR that would run happily on the available gas, without the motor being detuned.

Detuning the motor to the point where it doesn’t ping is a much worse evil(from a drivability standpoint) than if it had just been built with a lower CR that would run happily on the available gas, without the motor being detuned.

Totally agree. The thing is that the builder was given orders to build a motor that I could fill up with 91 octane 100% gas at any station in WI and have no detonation issues. That is why I am getting so frustrated. I didn't want a race motor.

 

[dadsbee]

What fuel did he run it smoothly on the dyno with?

 

[hunt2elk]

What fuel did he run it smoothly on the dyno with?

He says 91 octane.

 

[33 IMP]

Just for giggles, i checked on wallace racing calculators, to see how much they said you would lose, lowering your c.r. from10-1 to 9-1.
Entered 570hp with 10-1, dropped to 9-1, said your power would plummet all the way down to........


562.

 

[hunt2elk]

Just for giggles, i checked on wallace racing calculators, to see how much they said you would lose, lowering your c.r. from10-1 to 9-1.
Entered 570hp with 10-1, dropped to 9-1, said your power would plummet all the way down to........


562.

Isn't that something? How simple it would have been to build it the way I asked in the first place. And I have 595 hp now, so would still have had over 580. I am going to see if I can get ahold of him tomorrow to get the head gasket thickness and also if the pistons are dished and what the cc of them is. Then we can get an accurate cr on the Wallace site. My buddy thinks that the cam is causing the problems.

 

[Kern Dog]

Totally agree. The thing is that the builder was given orders to build a motor that I could fill up with 91 octane 100% gas at any station in WI and have no detonation issues. That is why I am getting so frustrated. I didn't want a race motor.

I said the same thing when I ordered the rotating assembly for my 493.
I didn't want something that ran right up to the edge of knocking where 1 point of octane made the difference.
I wanted a street engine that was fast.
If a car is used 90% of the time for racing, mixing in some 110 Sunoco is not a huge inconvenience.
During my frustrating experience, I posted about it on several Mopar forums thinking that if I cast a wide enough net, somewhere in all of it would be the answer. I was stubborn and didn't want to pull the engine to replace the pistons. Instead, I put in thicker head gaskets.
It worked but I suspect that this engine would make more power with dished pistons and quench.
Also, I asked what I should expect to see as evidence of detonation when I pulled the heads. I was told to look for broken ring lands, sharp holes in the pistons as if they had been hit with an ice pick and chunks missing. Check out what my pistons looked like:

After cleaning off the carbon buildup:

Zero damage anywhere. No discoloration. The head gaskets showed no burns, no defects. I dealt with what sounded like detonation but there was zero evidence of it. The 110 leaded gas allowed me to run the timing back up to 35 degrees and the car ran like Jessie Owens with no knocking but with 91 octane, it was back to detonation sounds. This is a mystery that I never figured out. Why did it make knocking noises and show zero evidence? Was it because I always lifted off the throttle the moment I heard knocking? Was there no damage because I didn't push it enough to let the damage develop ?
Sorry to hijack...I just thought I'd pass this along for whatever it is worth.

 

[beanhead]

Looks like you have a .080 mls gasket. (List shows .090 piston-to-head, with pistons .010 in the hole).
On a side note...it makes one wonder if the problem would still be happening at 9.9 if there was some quench there. I kind of agree with your friend that a different cam could have been used to close the intake later, but easy for me to say in hindsight and I will never know as much as Brian's forgotten...

 

[69 GTX]

My engine builder use the Icon D dished pistons to achieve a 9.9 ration. Like you, I said 91 octane. He went to the local station and got it. He told me after the dyno session that it might even run on 89. I also have the TF 240s. My guess is you have a flat top piston and it's not liking it. Also on the dyno they usually are getting nice cool air, that may also be part of the problem. It would be interesting if you would put a cool can in the fuel system to see if that made a difference. A phenolic spacer may also help too.